1. Field of the Invention
This invention relates in general to mooring equipment for vessels and in particular to chain support equipment for mooring legs of a spread mooring arrangement for a permanently moored storage vessel.
2. Description of the Prior Art
FIGS. 1 and 2 illustrate a prior art spread mooring system of British Patent 1,194,371 (published Jun. 10, 1970) having mooring legs 10 at the bow and stem of the vessel 20. FIG. 1 is a plan view of a storage vessel with two shuttle oil-tankers 22 berthed along side of it. FIG. 2 is a view similar to that of FIG. 1, but showing the storage vessel alone, skewed to port so that it can be pointed toward wind, waves, or current. The mooring legs must be lengthened and shortened appropriately to accommodate this rotation of the storage vessel from the position of FIG. 1 to that of FIG. 2.
FIGS. 3, 4, and 5 illustrate a prior art spread mooring system where anchor legs 10 at the bow and stern of a storage vessel extend from the sea floor through an opening in the bottom of the hull and pass through mooring insert tubes 120, one at the bow and the other at the stern of the vessel. The anchor legs of FIGS. 3, 4, and 5 cannot easily be lengthened/shortened to provide a skewed orientation of a vessel like that of FIGS. 1 and 2.
Other prior chain supports have included many moving parts and components which are prone to failure over time such as spring loaded flappers. Other prior chain support systems are deck mounted which require hull stiffening to transfer mooring loads. Such prior configurations require multiple sheaves, portable sheaves or vertical capstans which require a huge expanse of deck to reach all anchor legs from a central point.
A primary object of this invention is to provide a spread mooring arrangement where anchor legs enter the bottom of a vessel and extend upwardly through mooring insert tubes, one for each anchor chain, but can easily be lengthened or shortened to provide skewed headings of the vessel depending on wave, wind and current conditions.
Another object of the invention is to provide a trunnion style chain stopper into a swivel mounted chain support.
Another object of this invention is to provide a fixed self-contained modular unit for installation in a vessel for swivel chain support mounting.
Another object of this invention is to provide a self-contained modular unit which is arranged and designed for installation within the hull of a vessel, below decks, so as to avoid interference with deck houses, hose hauling and/or process equipment.
Another object of this invention is to provide a unit having a single installation winch at the stern, another at the bow, which can be moved among a plurality of anchor leg stations respectively at the stern and bow, to serve all anchor legs.
Another object of this invention is to provide a swivel mounted chain support where an anchor chain is pulled in and slides against a single trunnion guide face.
Another object of this invention is to provide a swivel mounted chain support with a single trunnion guide face where mooring loads between anchor chains and the vessel are transferred at the head of the trunnion support.
Another object of this invention is to provide a chain stopper in a single trunnion guide on a hull mounted chain support, rather than a deck mounted chain stopper, thereby providing a chain guidance to assume alignment in the lateral direction with the flapper of the chain stopper.
The objects identified above, along with other features and advantages result from providing a swivel mounted chain support, one for each anchor leg, at the bottom end of a mooring insert tube, so that as the vessel changes its heading, each anchor leg has its chain support turned to directly face its respective anchor leg, rather than entering the chain support at an angle. The mooring insert tube assembly, one for the bow, the other for the stern, is a fixed self-contained modular unit installed at the bow or stern of a vessel and includes one or more mooring insert tubes. A trunnion style chain stopper is mounted in a swiveling base to allow for rotation about a vertical axis similar to a standard fairlead sheave. A single winch is installed above the insert tube assembly with tracks to permit the winch to be moved from alignment with one mooring insert tube to another.